In oil and gas wells, it is known to employ packers to seal the gap between the outside diameter of a smaller pipe and the inside diameter of a larger pipe or casing. Packers can also be employed to anchor the smaller pipe to the larger pipe in order to prevent relative axial movement between the two pipes. On occasion, two smaller diameter non-concentric pipes or strings have to be anchored and sealed off inside a larger pipe; the multi-string packer used for this operation is commonly referred to as a "dual packer".
In oil wells where downhole electric pumps are used to pump the oil to the surface, a dual packer is commonly used where one of the pipes running through the packer is used to carry the oil flow and the other pipe is used to seal off around an electrical penetrator which carries electric power to the pump motor.
Packers used in downhole pumping applications may also have one or more additional small diameter pipes running through them for the purposes of gas venting, pressure sensing, or chemical injection. Such downhole pumping packers are usually of a type which can be generally described as "hydraulic set, straight pull release pump packers". This type of packer has a major disadvantage which is that once the packer is unset, it cannot be reset without first being withdrawn from the well and refurbished (e.g. by the replacement of fractured shear pins). Thus any electrical or other problem at the wellhead necessitating raising of the string (attached through completion tubing to the packer and to the pump which delivers through the completion tubing) in turn requires that the packer be unset and the entire completion tubing withdrawn from the well in order to refurbish the packer for a further setting. Since the completion tubing may have a length of about 10,000 feet (3 Kilometers), non-resettability of the pump packer is clearly a grave disadvantage. On the other hand, if the pump packer were resettable without having to be withdrawn from the well, the completion tubing need only be pulled back by about 50 feet (15 meters) to allow access to the wellhead equipment for repairs, followed by re-running of the 50 feet (15 meters) of tubing to return the packer to setting depth, and resetting of the packer. Thus a resettable pump packer would avoid the need for pulling of more than a minimal length of tubing and hence give very substantial savings in time and cost.
Resettability of multi-string packers in non-pump applications can similarly give rise to greater convenience of use and improvement in financial economy.
It is therefore an object of the invention to provide a multi-string packer which can be set downhole, unset, and reset at least once without withdrawal.